Hybrid switch circuit

Abstract

A hybrid switch circuit includes a hybrid switch that couples an input conductor connected to an AC power supply to an output conductor connected to a load. The hybrid switch includes a power semiconductor in parallel with an electromagnetic relay. A control circuit turns on the hybrid switch by turning on the power semiconductor at a zero-voltage crossing of the AC voltage to provide a conductive path and then closing the relay to provide a conductive bypass path that bypasses the power semiconductor. The control circuit turns off the hybrid switch by opening the relay and subsequently turning off the power semiconductor at a zero crossing of the load current. The control circuit operates in response to at least one switch control signal that indicates whether an operating fault condition exists.

What is claimed is: 
     
       1. A hybrid switch circuit for coupling an AC power supply to a load, comprising:
 a hybrid switch coupling an input conductor configured to be connected to the AC power supply to an output conductor configured to be connected to the load, the hybrid switch comprising:
 a power semiconductor switchable between on and off states in accordance with a power semiconductor control current, wherein, in the on state, the power semiconductor provides a conductive path for an AC current between input and output terminals thereof and, in the off state, the conductive path provided by the power semiconductor is opened; and 
 a relay having contacts in a conductive bypass path connected in parallel with the power semiconductor, the contacts being controllable between open and closed states in accordance with a relay control current taken from an output terminal of the power semiconductor, wherein, in the closed state, the relay provides a conductive bypass path between the input and output conductors that bypasses the power semiconductor; and 
 
 a control circuit configured to switch the hybrid switch from a non-conductive state to a conductive state, the control circuit comprising:
 a pair of control conductors terminating in a common connection to carry the power semiconductor control current electrically in parallel with the relay control current; and 
 at least one current switch coupled to at least one of the control conductors and switchable between conducting and non-conducting states in accordance with a state of at least one switch control signal, wherein, in the conducting state, the at least one current switch provides at least one conductive path for the power semiconductor control current and the relay control current and, in the non-conducting state, the at least one conductive path is opened. 
 
 
     
     
       2. The hybrid switch circuit of  claim 1 , wherein the control circuit is configured to switch the power semiconductor into the on state at zero-voltage crossings of an AC voltage of the AC power supply. 
     
     
       3. The hybrid switch circuit of  claim 1 , wherein the control circuit is further configured to switch the hybrid switch from the conductive state to the non-conductive state by switching a single current switch as the at least one current switch into a non-conducting state, responsive to which the relay control current decays in accordance with a first time constant to open the relay and the power semiconductor control current decays in accordance with a second time constant to switch the power semiconductor into the off state, wherein the second time constant is greater than the first time constant. 
     
     
       4. The hybrid switch circuit of  claim 3 , wherein the control circuit is configured to switch the power semiconductor into the off state at zero crossing of the AC current. 
     
     
       5. The hybrid switch circuit of  claim 1 , wherein the control circuit comprises:
 a switching device control circuit coupled to the input conductor on a supply side of the hybrid switch, the switching device control circuit being configured to switch the power semiconductor into the on and off states in accordance with a state of the flow of the power semiconductor control current in response to a hybrid switch control signal; and 
 a relay control circuit coupled to an output terminal of the power semiconductor, the relay control circuit being configured to open and close the relay in accordance with a state of the flow of the relay control current taken from the output terminal of the power semiconductor in response to the hybrid switch control signal, wherein the switching control circuit and the relay control circuit are connected to the common connection at a single current switch as the at least one current switch. 
 
     
     
       6. The hybrid switch circuit of  claim 5 , wherein, in response to the hybrid switch control signal being in an off state, the hybrid switch transitions from the conductive state to the non-conductive state by causing the relay control current to decay in the relay control circuit in accordance with a first time constant to open the relay and causing the power semiconductor control current to decay in the switching device control circuit in accordance with a second time constant to switch the power semiconductor into the off state, wherein the second time constant is greater than the first time constant. 
     
     
       7. The hybrid switch circuit of  claim 1 , wherein the control circuit comprises:
 a power semiconductor control circuit coupled to the input conductor on a supply side of the hybrid switch, the power semiconductor control circuit being configured to switch the power semiconductor into on and off states in response to a power semiconductor control signal, applied to a first one of the at least one current switch; and 
 a relay control circuit coupled to the input conductor on the supply side of the hybrid switch at the common connection with the power semiconductor control circuit, the relay control circuit being configured to open and close the relay in response to a relay control signal applied to a second one of the at least one current switch. 
 
     
     
       8. The hybrid switch circuit of  claim 1 , further comprising:
 at least one condition sensing circuit configured to detect at least one fault condition and to generate the at least one switch control signal indicative of whether the fault condition exists, the control circuit controlling the hybrid switch to be in the conductive or non-conductive state in accordance with the at least one switch control signal. 
 
     
     
       9. The hybrid switch circuit of  claim 8 , wherein the at least one condition sensing circuit comprises a plurality of condition sensing circuits whose outputs are connected in a wired-AND configuration to generate a hybrid switch control signal. 
     
     
       10. The hybrid switch circuit of  claim 8 , wherein the at least one condition sensing circuit comprises a microcontroller configured to generate a power semiconductor control signal to apply to a first current switch as the at least one current switch to control the power semiconductor and a relay control signal to apply to a second current switch as another of the at least one current switch to control the relay. 
     
     
       11. The hybrid switch circuit of  claim 8 , wherein the at least one condition sensing circuit comprises one or more of: an overvoltage circuit, an under-voltage circuit, an over-temperature circuit, a wiring fault circuit, and an over-current circuit. 
     
     
       12. The hybrid switch circuit of  claim 8 , wherein the at least one condition sensing circuit comprises:
 a regulated half wave rectifier circuit configured to generate a stable reference voltage; and 
 an operational amplifier including first and second inputs, wherein the stable reference voltage is coupled to one of the first and second inputs, and a signal indicating an operating condition is coupled to the other of the first and second inputs, wherein an output of the operational amplifier indicates whether the fault condition exists based on a comparison of the stable reference voltage and the signal indicating the operating condition. 
 
     
     
       13. The hybrid switch circuit of  claim 12 , further comprising:
 a first resistor coupling either the stable reference voltage or the signal indicating the operating condition to the first input of the operational amplifier; and 
 a second resistor coupling the first input of the operational amplifier to the output of the operational amplifier, wherein the first and second resistors cause the operational amplifier to operate with hysteresis in comparing the stable reference voltage to the signal indicating the operating condition. 
 
     
     
       14. A method of selectively connecting an AC power supply to a load by controlling a hybrid switch comprising at least one power semiconductor arranged in parallel with an electromagnetic relay, the method comprising:
 comparing at least one voltage indicating an operating condition and a reference voltage, the at least one voltage and the reference voltage being obtained between line and neutral conductors at an input of the AC power supply; 
 switching at least one current switch into a conducting state in response to at least one switch control signal indicating an absence of a fault condition as determined by the comparing, the conducting state of the at least one current switch providing a conductive path for a power semiconductor control current and a relay control current; 
 switching on the power semiconductor at a zero-voltage crossing of an AC voltage in an input conductor in response to the at least one current switch being switched into the conducting state to provide thereby a conductive path for an AC current between the input conductor and an output conductor connected to the load; and 
 switching the electromagnetic relay closed in response to the at least one current switch being switched into the conducting state to provide thereby a conductive bypass path between the input and output conductors that bypasses the power semiconductor. 
 
     
     
       15. The method of  claim 14 , further comprising:
 opening the electromagnetic relay to remove the conductive bypass path in response to an indication of the fault condition; and 
 after opening the electromagnetic relay, switching off the power semiconductor at a zero crossing of a load current to remove the conductive path between the input and output conductors. 
 
     
     
       16. The method of  claim 14 , further comprising:
 generating the at least one switch control signal indicating an absence or presence of the fault condition by comparing the voltage indicating the operating condition to the reference voltage using an operational amplifier. 
 
     
     
       17. The method of  claim 14 , further comprising:
 generating the at least one switch control signal indicating an absence or presence of the fault condition from outputs of a plurality of condition sensing circuits that are connected in a wired-AND configuration. 
 
     
     
       18. The method of  claim 14 , further comprising:
 generating the at least one switch control signal, indicating an absence or presence of the fault condition, with switch control circuit that detects at least one of the following fault conditions: an overvoltage condition, an under-voltage condition, an over-temperature condition, a wiring fault condition, and an over-current condition. 
 
     
     
       19. The method of  claim 14 , further comprising:
 generating a power semiconductor control signal to control the power semiconductor in accordance with an absence or presence of the fault condition detected by a microcontroller; and 
 generating a relay control signal to control the relay in accordance with the absence or presence of the fault condition detected by the microcontroller. 
 
     
     
       20. A power filter circuit, comprising:
 a power conditioning circuit configured to suppress disturbances in an AC power supply, the power conditioning circuit comprising:
 a diverter stage electrically coupled in parallel with the AC power supply; 
 a filter stage electrically coupled to the diverter stage to produce filtered AC power on an input conductor; 
 a clamp stage electrically coupled in parallel with a load at an output conductor; 
 
 a hybrid switch coupling the input conductor to the output conductor, the hybrid switch comprising:
 a power semiconductor switchable between on and off states in accordance with a power semiconductor control current, wherein, in the on state, the power semiconductor provides a conductive path for filtered AC current between the input and output conductors and, in the off state, the conductive path provided by the power semiconductor is opened; and 
 a relay having contacts in a conductive bypass path connected in parallel with the power semiconductor, the contacts being controllable between open and closed states in accordance with a relay control current, wherein, in the closed state, the relay closes the conductive bypass path between the input and output conductors that bypasses the power semiconductor; and 
 
 a hybrid switch control circuit comprising:
 at least one condition sensing circuit configured to generate at least one switch control signal whose state indicates whether an operating condition constitutes a fault condition, the condition sensing circuit being connected in parallel with the AC power supply to determine wiring faults and to the input conductor to determine faults in the filtered AC power, wherein the at least one switch control circuit is configured to switch the power semiconductor into the on state at a zero-voltage crossing of filtered AC voltage on the input conductor and, subsequently, to switch the electromagnetic relay into the closed state in accordance with flow of the relay control current. 
 
 
     
     
       21. The power filter circuit of  claim 20 , further comprising:
 an alternate output conductor configured to be connected to the load, the alternate output conductor being coupled to the input conductor on an input side of the hybrid switch, thereby bypassing the hybrid switch. 
 
     
     
       22. The power filter circuit of  claim 20 , wherein the power filter stage is configured to suppress at least one of: voltage transients, electromagnetic interference (EMI), and radio frequency interference (RFI). 
     
     
       23. The power filter circuit of  claim 20 , wherein the at least one condition sensing circuit comprises a microcontroller. 
     
     
       24. The power filter circuit of  claim 20 , wherein the at least one condition sensing circuit comprises a plurality of operational amplifiers to compare a reference voltage generated from the filtered AC voltage with voltages indicative of the faults in the filtered AC power. 
     
     
       25. The hybrid switch circuit of  claim 10 , wherein the microcontroller is configured to apply another state of the power semiconductor control signal to the first current switch to control the power semiconductor into the off state upon the relay being controlled into the closed state. 
     
     
       26. The method of  claim 14  further comprising:
 switching the power semiconductor off in the absence of the fault condition upon the relay being closed. 
 
     
     
       27. The power filter circuit of  claim 20 , wherein the at least one switch control circuit is configured to switch the power semiconductor into the off state upon the electromagnetic relay being in the closed state for a predetermined time period absent of the fault condition.